I've been farming heroic bounties for hours and I am never rewarded with a red border weapon. If bungie didn't want us to craft these weapons, why in the hell are they so hard to aquire? I've tried all farming methods, none of them are dropping red border weapons.
I've only had red border weapons drop from Public Events and Nimrod rank ups. I was farming those gold patrols but gave up ages ago.
Do Public Events while completing bounties, patrols and opening chests and gathering the region materials for Pneumonia rank, best way but still takes ages.